This disclosure relates to an image forming apparatus and a method for correcting color misregistration performed by the image forming apparatus.
Image forming apparatuses, typified by digital multi-function peripherals, read an image of an original document by using an image reading unit, and then emit light to a photoconductor in an image forming unit based on the read image to form an electrostatic latent image on the photoconductor. Then, a charged developer, including toner and other components, is applied onto the formed electrostatic latent image to make it into a visible image that is in turn transferred onto a sheet of paper and fixed. The sheet with the image fixed thereon is discharged outside the image forming apparatus.
Some image forming apparatuses are full-color image forming apparatuses that form full color images by superimposing colors, e.g. yellow, cyan, magenta, and black. Such full-color image forming apparatuses need to correct color misregistration at predetermined timings for the purpose of improving color development and color reproducibility.
There are some well-known techniques of correcting color misregistration for image forming apparatuses. A typical image forming apparatus, which forms an image of different colors on a recording medium based on image data, includes a latent image forming unit that forms a latent image by scanning a plurality of photoconductors with light beams based on the image data, a pattern forming unit that forms a first pattern of strip marks and a second pattern of strip marks used to measure misalignment of each color, the marks in the first and second patterns each corresponding to one of the colors and arranged in parallel to each other, and the marks in the first pattern being spaced at predetermined intervals and the marks in the second pattern being spaced at wider intervals than the predetermined intervals, a misalignment measurement unit that measures an amount of misalignment of each of the marks in the first and second patterns formed by the pattern forming unit, and a misalignment correction unit that corrects the misalignment of each color based on the amount of misalignment measured by the misalignment measurement unit. If the amount of misalignment of the marks in the first pattern, which has been measured by the misalignment measurement unit, is greater than a predetermined value, the misalignment correction unit causes the pattern forming unit to form the second pattern of the marks, causes the misalignment measurement unit to measure the amount of misalignment of the marks of each color in the second pattern, and controls the latent image forming unit to compensate for the misalignment based on the measured misalignment amount to form a corrected image.